1. Field
The present invention relates to a rocker arm provided in an internal combustion engine for opening and closing a valve.
2. Related Art
Japanese patent application publication JP-A-2002-161717 discloses a conventional rocker arm of the above-described type having an arm body which is elongate in a front-back direction. The arm body has a front end formed with a valve abutting portion on which a valve is caused to abut and a rear end formed with a support receiving portion which is supported on an upper end of a pivot mounted on a cylinder head. The arm body further has a middle portion formed with a storage portion in which a roller is stored.
When a roller is driven by a cam which abuts on the roller, the rocker arm is swung with an upper end of the pivot serving as a fulcrum, whereby the valve is lifted. In this case, the upper end of the pivot is formed with a concave sphere, and the support receiving portion has an underside formed with a convex sphere. The concave sphere of the pivot acts as a receiving pan which receives lubricant oil, reserving the lubricant oil. The lubricant oil lubricates surfaces of both concave and convex spheres so that sliding friction between the rocker arm and the pivot can be reduced.
Peripheral or circumferential surfaces of the roller and the cam also need to be lubricated with lubricant oil for reduction in the sliding friction between the roller and the cam. In this case, for example, a flow path is formed in an upper surface of the arm body so that the lubricant oil flows therethrough toward the roller storage portion. The aforesaid gap is defined between an opening edge of the roller storage portion and a circumferential surface of the roller. The lubricity of the lubricant oil needs to be improved by reducing the gap. However, as shown in FIG. 5, a roller 4 has a peripheral surface further having both widthwise end corners to which parts A of an opening edge 3 are opposed respectively. When the opening edge 3 of the roller storage portion is to be formed along an outer edge of the roller 4 while the aforesaid gap is reduced, each part A needs to be formed so as to have such a small radius that each part A makes a right angle. Accordingly, it is difficult to improve a machining accuracy of each part A.
On the other hand, the machinability can be improved when the aforesaid gap between the roller storage portion and the roller 4 is wholly increased. In this case, however, there is a case where the lubricant oil cannot reach the circumferential surface of the roller 4. Accordingly, increasing the aforesaid gap is undesirable. More specifically, the machinability of the rocker arm 2 is reduced when preference is given to the lubricity between the roller 4 and the cam, whereas the lubricity between the roller 4 and the cam is reduced when preference is given to the machinability of the rocker arm 2. Thus, it is difficult to satisfy both lubricity and machinability at the same time.